Sì yuè means “April”, wǔ yuè means “May”. The months are numbered too: April is the fourth month, May the fifth. You already know the numbers – the only new word is the one for month.
On a calendar open at April stands a yoghurt with a small eyelet. Inside it a radio plays sharp music – that gives you yuè, with the sharp music marking the falling tone. Four and month give you sì yuè, five and month wǔ yuè. In less than two minutes you can now say the months from January to October.